Acrylic acid is a raw material monomer for polyacrylic acids or acrylic acid-based copolymers. With increase in the amount of water-absorbing resins (polysodium acrylate) used, its production amount is increasing. The acrylic acid is usually manufactured by synthesizing acrolein from propylene, which is a petroleum-derived raw material, and subjecting the acrolein to catalytic gas phase oxidation to be converted into an acrylic acid (for example, patent document 1).
However, there is a concern that the petroleum-derived raw materials will be depleted in future. From such reasons, studies have been made aimed at obtaining an unsaturated carboxylic acid from biomass. For example, a method for synthesizing an unsaturated carboxylic acid or an ester thereof from an ammonium salt of a hydroxycarboxylic acid is disclosed in patent document 2.